Advanced Characterization Techniques for Quantifying and Modeling Deformation: Session II
Sponsored by: TMS Extraction and Processing Division, TMS Structural Materials Division, TMS: Advanced Characterization, Testing, and Simulation Committee, TMS: Materials Characterization Committee
Program Organizers: Mariyappan Arul Kumar, Los Alamos National Laboratory; Irene Beyerlein, University of California, Santa Barbara; Wolfgang Pantleon, Technical University of Denmark; C. Tasan, Massachusetts Institute of Technology; Olivia Underwood Jackson, Sandia National Laboratories

Monday 2:00 PM
February 28, 2022
Room: 207A
Location: Anaheim Convention Center

Session Chair: Penghui Cao, University of California, Irvine; Aeriel Murphy-Leonard, Ohio State University

2:00 PM  Invited
Quantifying Damage Evolution during In-situ Loading of Additive Manufactured 316L Stainless Steel Using High Energy X-rays : Aeriel Murphy-Leonard1; David Rowenhorst2; 1Ohio State University; 2US Naval Research Laboratory
    The evolution of damage, texture, and strain in additive manufactured (AM) 316L stainless steel was investigated during in-situ tensile loading using high energy X-rays. Synchrotron X-ray computed tomography (measurements were performed to determine the initial porosity and monitor the evolution of porosity during tensile loading as well as detect the initiation and growth of voids from pre-existing pore defects in the specimens. Far-field X-ray diffraction measurements were performed to quantify crystallographic texture and the distribution of internal elastic strains during loading. As a result of tensile deformation, a strong {111} + {200} double fiber texture develops at high tensile strains and remains until fracture. XCT results confirmed that pores were found to have an asymmetric or irregular morphology. At high tensile strains, the massive accumulation of internal damage at these pores eventually connected to the surface reducing the ductility in these thin-walled AM samples and resulting in final failure.

2:30 PM  
Line Profile Analysis from In Situ Synchrotron X-ray Diffraction to Study the Microstructural Evolution during Elasto-plastic Transition in Nickel with Bimodal Grain Structure: Elis Sjogren1; Wolfgang Pantleon2; Ulrich Lienert3; Zoltan Hegedüs3; Kei Ameyama4; Dmyto Orlov1; 1Lund University; 2Technical University of Denmark; 3Deutsches Elektronen-Synchrotron; 4Ritsumeikan University
    Materials with bimodal grain size distributions have an attractive combination of strength and ductility. The elasto-plastic transition of such materials requires thorough investigations. In this study, nickel with bimodal grain structure was deformed in tension until 4% strain while recording powder diffraction patterns at the synchrotron beamline P21.2 at PETRA III. Line profile analysis based on powder diffraction data enables quantification of stress states and lattice defect densities in different phases in multi-phase materials. Bimodal size distributions in single-phase materials add extra complexity due to the absence of differences in composition and crystal structure. We will present a method for acquiring and separating diffraction profiles originating individually from coarse and fine grains. The analysis reveals a stress-strain behavior of both grain fractions similar to their homogenous counterparts apart from an increased work-hardening rate of the coarse grains. More advanced line profile analysis will provide further insights on the elasto-plastic transition.

2:50 PM  
Recent Advances and Applications of Lab-based Diffraction Contrast Tomography: Jette Oddershede1; Jun Sun1; Florian Bachmann1; Hrishikesh Bale2; Erik Lauridsen1; 1Xnovo Technology; 2Carl Zeiss X-ray Microscopy Inc.
    Adequate experimental statistics is essential for improving and validating microstructural simulations to ensure the handshake between modelling and experiment. Here we present the next generation of lab-based diffraction contrast tomography (DCT), introducing advanced scanning schemes to seamlessly acquire data and reconstruct grain maps of longer, larger, high aspect ratio samples. This unlocks access to massive sample volumes – up to three orders of magnitude larger than traditional 3D-EBSD methods – and delivers true sample representivity. Additionally, due to its non-destructive operation, lab-based DCT enables tracking the evolution of microstructure through processes such as annealing or grain growth. The technique and examples will be presented highlighting the use of large volume, large grain statistics.

3:10 PM  
Time Resolved Evolution of the 3D Nanoporous Structure of Sintered Ag by X-ray Nanotomography: Role of the Interface with a Copper Substrate: Xavier Milhet1; Kokouvi N'Tsouaglo1; Jerome Colin1; Loic Signor1; Azdine Nait-Ali1; Juan Creus2; Mikael Gueguen1; Marc Legros3; 1Prime Institute CNRS ENSMA; 2LaSIE Universite La Rochelle; 3CEMES - CNRS - Toulouse
    The evolution of the nanoporous structure of sintered silver during high temperature aging, ranging from 200°C to 350°C is investigated by in-situ Computed X-Ray Tomography. Investigations were performed on both pure sintered silver and specimens containing a silver/copper interface. It is shown that while pore evolution is driven by diffusion (Oswald ripening), the presence of an interface promotes faster growth kinetics until a deviation from Oswald ripening occurs. This evolution can be explained considering the conjugated effects of the thermal stresses and surface energy on the diffusion process. Preliminary finite elements modeling has been performed using the real microstructure in order to investigate on the relationship between mechanical loading and nanoporous structure evolution.

3:30 PM Break

3:45 PM  Invited
Fundamental Deformation Mechanisms in Metals with Gradient Structure and Multi-principal Element Alloys: Penghui Cao1; 1University of California, Irvine
    Mechanistic prediction of mechanical behaviors of materials requires a fundamental understanding of the underpinning deformation mechanisms. We will discuss our findings of deformation processes at atomistic to nanoscopic scales in two classes of materials - gradient nano-grained metals and multi-principal element alloys, using multiscale atomistic simulations coupled with in-situ testing and characterization. We show that, for gradient nanostructured copper, increasing the degree of structure gradient can promote dislocation-mediated intragranular plasticity and mitigate the grain boundary-mediated softening. Concerning multi-principal element alloys, we integrate atomistic modeling, in-situ SEM straining, and TEM characterization to reveal the role of short-range chemical order on dislocation slip, twinning, and martensitic transformation. The microstructure and local strain evolution as a result of these deformation processes will be discussed.

4:15 PM  
Cores of 1/2<110>-type Dislocations in the CrMnFeCoNi High-entropy Alloy Investigated by STEM, the Center of Symmetry and the Nye Tensor Mapping Techniques: Milan Heczko1; Veronika Mazánová1; Roman Gröger2; Tomáš Záležák2; Mohammad Hooshmand3; Easo George4; Michael Mills1; Antonín Dlouhý2; 1The Ohio State University; 2Institute of Physics of Materials CAS; 3University of California; 4Oak Ridge National Laboratory
    The influence of small pre-strains on the elevated-temperature stability and microstructure of the equiatomic CrMnFeCoNi high-entropy alloy is investigated. Attention is given to whether any of the alloy elements segregate to individual dislocations. Samples were deformed in tension at room temperature to plastic strains of 0.2 and 2.3%, and subsequently annealed at 973 K for 800 hours. The pre-strains activated planar slip of 1/2<110>-type dislocations on {111}-type glide planes. Interactions of this planar slip with special Σ3 grain boundaries formed a number of dislocation segments with a <110>-type crystallographic orientation suitable for a credible end-on analysis. Results of atomic resolution STEM and Super-X EDS experiments combined with the center of symmetry and the Nye-tensor mapping suggest that the indicated thermo-mechanical treatments did not cause any chemical changes to dislocation cores. Important implications of presented results on the mechanisms of high-temperature creep in this class of materials are discussed.

4:35 PM  
Local Phase Transformation at Microtwins and Planar Defects in Creep Deformed Ni-Base Superalloys: Ashton Egan1; Fei Xue2; Longsheng Feng1; Shakthipriya Baskar Kannan1; Gregory Sparks3; Timothy Smith4; Emmanuelle Marquis2; Yunzhi Wang1; Maryam Ghazisaeidi1; Michael Mills1; 1Ohio State University; 2University of Michigan; 3Air Force Research Laboratory; 4NASA Glenn Research Center
    In the intermediate temperature creep regime of Ni-based superalloys (~700 °C) deformation is dominated by thermal activation of planar defects and microtwinning, where diffusion mediated reordering and segregation of key elements play a major role in controlling strain rate. Of particular interest are alloys with Local Phase Transformation (LPT) strengthening, a dynamic process whereby phases form along defects. During this study the strengthening effects of several alloys, including specifically oriented single crystal NA1 and ME501, in the LPT composition regime are explored to elucidate atomic scale processes. Advanced characterization of active deformation mechanisms and LPT was accomplished using probe corrected Scanning Transmission Electron Microscopy (STEM), atomic scale Energy Dispersive X-Ray Spectroscopy (EDS), TEM-correlated Atom Probe Tomography (APT), and multislice STEM modeling. Mesoscale characterization utilizing Scanning Electron Microscopy (SEM) based Controlled Electron Channeling Contrast Imaging (cECCI) support atomic scale analyses. Understanding LPT effects inform both multiscale modeling efforts and alloy development.

4:55 PM  
Investigation of Dislocation Structures in an Al-Li Binary Alloy via High Resolution X-ray Characterization Techniques: Sven Gustafson1; Wolfgang Ludwig2; Katherine Shanks3; Carsten Detlefs4; Michael Sangid1; 1Purdue University; 2University Lyon I; 3Cornell High Energy Synchrotron Source; 4European Synchrotron Radiation Facility
    During cyclic loading, dislocations accumulate at microstructural features such as grain boundaries and form structures within the interior of individual grains; such structures lead to intragranular variations of elastic strain and orientation. With increasing cycles, these variations lead to potentially large stress/strain gradients and inevitably will affect the fatigue performance of the material. Grain averaged elastic strains were tracked via high energy X-ray diffraction microscopy during high cycle fatigue loading of a polycrystalline, Al-Li binary alloy. Following cyclic loading, individual grain(s) within the bulk of the specimen were further probed by dark field X-ray microscopy, a high-resolution X-ray characterization technique, to characterize the 3D elastic strain and orientation fields around internal dislocation structures. This study will provide new insights of fatigue induced dislocation structures, such as persistent slip bands, in the bulk of polycrystalline materials, which are unable to be captured with standard 2D surface or destructive techniques.